The present invention relates generally to the nonenzymatic glycosylation of proteins, and particularly to the discovery of binding partners to advanced glycosylation endproducts such as AGE receptors, that may serve in the diagnosis and treatment of conditions in which the presence or activity of such advanced glycosylation endproducts may be implicated.
Glucose and other reducing sugars react non-enzymatically with the amino groups of proteins in a concentration-dependent manner. Over time, these initial Amadori adducts undergo further rearrangements, dehydrations and cross-linking with other proteins to accumulate as a family of complex structures which are referred to as Advanced Glycosylation Endproducts (AGEs). Although this chemistry has been studied by food chemists for many years, it was only in the past decade that the presence of AGEs in living tissue has been established. The excessive deposition of these products on structural proteins as a function of age and elevated glucose concentration, taken together with evidence of effective prevention of tissue pathology by an AGE inhibitor, aminoguanidine, has lent support to the hypothesis that the formation of AGEs plays a role in the long term complications of aging and diabetes.
Since the amount of AGEs found in human tissues is less than could be predicted from protein/glucose incubation studies in vitro, the applicants herein proposed several years ago that there might be normal mechanisms to remove those long-lived proteins which had accumulated AGEs in vivo. Particularly, and as set forth initially in Parent application Ser. No. 907,747, and the above-referenced applications that have followed, monocytes/macrophages and endothelial cells were found to display high affinity surface binding activity specific for AGE moieties independent of the protein which was AGE-modified. This AGE-receptor was shown to differ from other known scavenger receptors on these cells.
In addition, an endogenous means for the in vivo elimination or removal of advanced glycosylation endproducts was set forth, and corresponding diagnostic applications involving the receptors and including a specific receptor assay were also proposed.
Following this determination, the applicants herein have sought to further investigate the identity and role of advanced glycosylation endproduct receptors and possible binding partners, and any consequent diagnostic and therapeuptic implications of these investigations, and it is toward this end that the present invention is directed.
The AGE-specific receptor system now includes a variety of tissues and cell types in addition to monocyte/macrophages for which receptor-mediated AGE-protein internalization and digestion was first described. Endothelial, mesangial cells and fibroblasts have since been shown to specifically bind AGE-modified protein. In macrophages, AGE-protein uptake is accompanied by the release of a variety of potent cytokines and growth factors, which may coordinate processes of normal tissue remodeling. The other cell types do not bind the model compound AGE, FFI, nor are they known to release cytokines and growth factors in response to AGE-ligand binding, but each cell type does display distinct functional responses. For example, endothelial cells exhibit enhanced surface procoagulant activity and permeability; and mesangial cells display enhanced matrix protein synthesis; while human fibroblasts increase proliferation upon exposure to AGEs.